Finfet device and method of forming the same

ABSTRACT

The embodiments of the disclosure provide a FinFET. The FinFET includes a substrate, a first gate stack and a second gate stack. The substrate has a first fin and a second fin. The first gate stack is across the first fin and extends along a widthwise direction of the first fin. The second gate stack is across the second fin and extends along a widthwise direction of the second fin. A bottommost surface of the first gate stack is lower than a bottommost surface of the second gate stack, and a first gate height of the first gate stack directly on the first fin is substantially equal to a second gate height of the second gate stack directly on the second fin.

BACKGROUND

The semiconductor integrated circuit (IC) industry has experienced exponential growth. Technological advances in IC materials and design have produced generations of ICs where each generation has smaller and more complex circuits than the previous generation. In the course of IC evolution, functional density (i.e., the number of interconnected devices per chip area) has generally increased while geometry size (i.e., the smallest component (or line) that may be created using a fabrication process) has decreased. This scaling down process generally provides benefits by increasing production efficiency and lowering associated costs. Such scaling down has also increased the complexity of manufacturing ICs and, for these advances to be realized, similar developments in IC manufacturing are needed.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the following detailed description when read with the accompanying figures. It is noted that, in accordance with the standard practice in the industry, various features are not drawn to scale. In fact, the critical dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion.

FIG. 1 is a three-dimensional view illustrating a semiconductor structure in intermediate stage for forming a fin-type field effect transistor (FinFET) device according to some embodiments of the disclosure.

FIG. 2 to FIG. 6, and FIG. 7A/7B to FIG. 13A/13B are cross-sectional views illustrating a method of forming a FinFET device, according to some embodiments of the disclosure.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, or examples, for implementing different features of the provided subject matter. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. For example, the formation of a second feature over or on a first feature in the description that follows may include embodiments in which the second and first features are formed in direct contact, and may also include embodiments in which additional features may be formed between the second and first features, such that the second and first features may not be in direct contact. In addition, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath”, “below”, “lower”, “on”, “over”, “overlying”, “above”, “upper” and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. The spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. The apparatus may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein may likewise be interpreted accordingly.

In some embodiments in which the semiconductor device is fin-type field effect transistor (FinFET) device, the fins may be patterned by any suitable method. For example, the fins may be patterned using one or more photolithography processes, including double-patterning or multi-patterning processes. Generally, double-patterning or multi-patterning processes combine photolithography and self-aligned processes, allowing patterns to be created that have, for example, pitches smaller than what is otherwise obtainable using a single, direct photolithography process. For example, in one embodiment, a sacrificial material layer is formed over a substrate and patterned using a photolithography process. Spacers are formed alongside the patterned sacrificial material layer using a self-aligned process. The sacrificial material layer is then removed, and the remaining spacers may then be used to pattern the fins.

A semiconductor device (e.g. FinFET device) and method of forming the same are provided in accordance with some embodiments of the disclosure. Various embodiments are directed to provide a FinFET device including a plurality of gate structures, which are formed to have substantially the same gate heights, so as to improve device performance. Throughout the various views and illustrative embodiments, like reference numbers are used to designate like elements.

FIG. 1 is a three-dimensional view illustrating a semiconductor structure 10 in intermediate stage for forming a FinFET device, in accordance with some embodiments of the disclosure.

Referring to FIG. 1, the semiconductor structure 10 includes a substrate 100 having a plurality of fins 101. The fins 101 protrude from a top surface TS of the substrate 100 in a direction D3 and extend along a direction D1. In some embodiments, the fins 101 are arranged along a direction D2 perpendicular to the direction D1 and spaced from each other. In other words, the lengthwise direction of the fin 101 is along the direction D1, and the widthwise direction of the fin 101 is along the direction D2. An isolation structure 102 is formed on the substrate 100 and laterally covering lower portions of the fins 101. One or more gate structures, such as dummy gate structure DG1 and DG2 are formed over the substrate 100 and across the plurality of fins 101 and the isolation structure 102. In some embodiments, the dummy gate structures DG1 and DG2 extend along the widthwise direction (i.e. direction D2) of the fins 101. It is noted that, the number of fins 101 and dummy gate structures shown in the figures are merely for illustration, and the disclosure is not limited thereto.

FIG. 2 to FIG. 13 are cross-sectional views illustrating various stages of manufacturing method of a FinFET device according to some embodiments of the disclosure, wherein FIG. 2 to FIG. 6, and FIG. 7A/7B to FIG. 8A/8B illustrates the intermediate stages for forming the semiconductor structure 10 shown in FIG. 1, and FIG. 9A/9B to FIG. 13A/13B illustrate the subsequent processes performed on the semiconductor structure 10 for forming the FinFET device. FIG. 2 to FIG. 6 and FIG. 7A to FIG. 13A are cross-sectional views of intermediate stages in the manufacturing of the FinFET, and are shown along I-I′ line of FIG. 1. FIG. 9B to FIG. 13B are cross-sectional views of intermediate stages in the manufacturing of the FinFET, and are shown along II-II′ line (in region R1) and line (in region R2) of FIG. 1.

Referring to FIG. 1 and FIG. 2, a substrate 100 is provided. The substrate 100 is a semiconductor substrate, which may be doped (e.g., with a p-type or an n-type dopant) or undoped. The substrate 100 may be a semiconductor wafer, such as a silicon wafer. Other substrates, such as a multi-layered or gradient substrate may also be used. In some embodiments, the material of the substrate 100 may include silicon; germanium; a compound semiconductor including silicon carbide (SiC), gallium arsenic (GaAs), gallium phosphide (GaP), indium phosphide (InP), indium arsenide (InAs), and/or indium antimonide (InSb); an alloy semiconductor including SiGe, GaAsP, AlInAs, AlGaAs, GaInAs, GaInP, and/or GaInAsP; or combinations thereof.

In some embodiments, the substrate 100 is patterned to form a plurality of fins 101. The fins 101 are semiconductor strips arranged along the direction D2 and spaced from each other. The widths of fins 101 may be the same or different, and the spacings between different fins 101 may be the same or different. In some embodiments, the substrate 100 is patterned to include multiple groups of fins having different patterns (e.g. different size, spacing, etc.) disposed in different regions of the substrate 100. For example, the substrate 100 includes a first group of fins 101 a in a first region R1 and a second group of fins 101 b in a second region R2. The first region R1 and the second region R2 may be immediately adjacent to each other, or spaced from each other by other regions. The fins 101 a and the fins 101 b have different patterns. In some embodiments, the spacing S1 between two adjacent fins 101 a is different form (e.g., larger than) the spacing S2 between two adjacent fins 101 b. For example, the ratio of the spacing S2 to the spacing S1 may range from 0.009 to 0.5. Although two groups of fins having different patterns, and two fins are shown to be included in each group of fins for illustration, the disclosure is not limited thereto. The substrate 100 may be patterned to have any suitable number of fin groups. In some embodiments, more than two groups of fins having different patterns may be formed, and each group of fins may include any suitable number of fins. In some embodiments, the top surfaces of the fins 101 a and 101 b are substantially coplanar with each other.

Referring to FIG. 3, an insulating material 102′ is formed on the substrate 100 and between the neighboring fins 101. In some embodiments, the insulating material 102′ is formed to cover top surfaces and sidewalls of the fins 101. The insulation material 102′ may include an oxide such as silicon oxide, a nitride such as silicon nitride, the like, or a combination thereof, and may be formed by a high density plasma chemical vapor deposition (HDP-CVD), a flowable CVD (FCVD), the like, or a combination thereof. Other insulation materials formed by any acceptable process may also be used. In some embodiments, an anneal process may be performed once the insulation material is formed.

Referring to FIG. 4, a planarization process is performed to remove excess portions of the insulation material 102′ over the top surfaces of the fins 101. In some embodiments, the planarization process includes a chemical mechanical polish (CMP), an etch back process, combinations thereof, or the like. As such, the top surfaces of the fins 101 are exposed and may be substantially coplanar with the top surface of the insulation material 102′.

Referring to FIG. 4 and FIG. 5, the insulation material 102′ is further recessed to form an isolation structure 102, such that upper portions of the fins 101 are exposed and protrude from the top surfaces of the isolation structure 102. In some embodiments, the isolation structure 102 is Shallow Trench Isolation (STI) structure. An acceptable etching process (such as, dry etching, wet etching or a combination thereof) may be performed to remove portions of the insulation material 102′ laterally covering upper portions of the fins 101, such that the insulation material 102′ is recessed.

In some embodiments, during the etching process, since the spacing S1 between neighboring fins 101 a in the first region R1 is larger than the spacing S2 between neighboring fins 101 b in the second region R2, the etchant or etching gas used for etching the insulation material 102′ is much easier to enter into the gap G1 between neighboring fins 101 a compared to entering into the gap G2 between neighboring fins 101 b. Accordingly, the etching rate of the insulation material 102′ in the first region R1 is larger than the etching rate of the insulation material 102′ in the second region R2, and therefore, the removal amount of the insulation material 102′ in the first region R1 is larger than the removal amount of the insulation material 102′ in the second region R2. As such, the isolation structure 102 is formed to have an uneven top surface and have different heights in the regions R1 and R2.

Referring to FIG. 5, in some embodiments, the isolation structure 102 includes the isolation structure 102 a in the first region R1 and the isolation structure 102 b in the second region R2. The isolation structure 102 a may have a top surface TS1 lower than a top surface TS2 of the isolation structure 102 b. In other words, the height H1 of the isolation structure 102 a is less than the height H2 of the isolation structure 102 b, and the height of the portion of the fin 101 a protruding above the top surface TS1 of the isolation structure 102 a is greater than the height of the portion of the fin 101 b protruding above the top surface TS2 of the isolation structure 102 b. In some embodiments, the ratio of the height H2 to the height H1 is larger than 1 due to the difference between spacings S1 and S2, and may range from 1 to 1.6 (excluding 1), for example. In some embodiments, each of the top surface TS1 and the top surface TS2 has a flat surface as illustrated, a convex surface, a concave surface (such as dishing), or the like.

Referring to FIG. 6, a dielectric layer 105 is formed to cover the fins 101. The dielectric layer 105 may include silicon oxide, silicon nitride, a combination thereof, or the like. In some embodiments, the dielectric layer 105 is a conformal layer, that is, the dielectric layer 105 has a substantially equal thickness extending along the region on which the dielectric layer 105 is formed. In some embodiments, the dielectric layer 105 is formed by a suitable deposition process such as CVD, atomic layer deposition (ALD), or the like, and extends along the surfaces of the fins 101 and the isolation structure 102. In alternative embodiments, the dielectric layer 105 may be formed by thermal oxidation process and formed on the fins 101 without being formed on the isolation structure 102.

Referring to FIG. 7A and FIG. 7B, a dummy gate layer 106′ is formed on the dielectric layer 105. In some embodiments, the combination of the dummy gate layer 106′ and the dielectric layer 105 may be referred to as dummy gate material. The dummy gate layer 106′ may be a conductive material and may be selected from a group including amorphous silicon, polycrystalline-silicon (polysilicon), poly-crystalline silicon-germanium (poly-SiGe), or the like or combinations thereof. In one embodiment, amorphous silicon is deposited and recrystallized to create polysilicon. The dummy gate layer may be formed by a deposition process such as physical vapor deposition (PVD), chemical vapor deposition (CVD), or other suitable deposition process.

The dummy gate layer 106′ overlies the fins 101 and the isolation structure 102. In some embodiments, since the isolation structure 102 b in the second region R2 is higher than the isolation structure 102 a in the first region R1, the dummy gate layer 106′ in the second region R2 is formed to have a top surface higher than a top surface of the dummy gate layer 106′ in the first region R1. In other words, the dummy gate layer 106′ includes a first portion P1′ in the first region R1 and a second portion P2′ in the second region R2, and the top surface TP2′ of the second portion P2′ is higher than the top surface TP1′ of the first portion P1′. In some embodiments, the top surfaces of the fins 101 a and 101 b are substantially coplanar with each other, and a thickness T2′ of the second portion P2′ directly over the fins 101 b is larger than the thickness T1′ of first portion P1′ directly over the fins 101 a. The thickness of the dummy gate layer 106′ on the corresponding fin 101 is related to the gate height of the subsequently formed gate electrode.

Referring to FIG. 7A, in some embodiments, each of the top surfaces TP1′ and TP2′ of the first and second portions P1′/P2′ of the dummy gate layer 106′ are undulated or uneven due to the uneven surfaces of underlying layers, and the top surface TP1′ may be more undulated than the top surface TP2′.

Referring to FIG. 8A and FIG. 8B, a planarization process is performed on the dummy gate layer 106′, so as to form a dummy gate layer 106 having substantially flat/planar top surface. In some embodiments, after the planarization process is performed, the dummy gate layer 106 includes a first portion P1 in the first region R1 and a second portion P2 in the second region R2, and the top surface TP1 of the first portion P1 is substantially coplanar with the top surface TP2 of the second portion P2. In other words, the thickness T1 of the first portion P1 directly over the fins 101 a is substantially equal to the thickness T2 of the second portion P2 directly over the fins 101 b. In some embodiments, the thickness T1/T2 partially defines the gate heights of the subsequent formed gate stacks in the first and second regions R1/R2.

In some embodiments, the planarization process may include a CMP process and may remove a part of the second portion P2′ and/or a part of the first portion P1′ of the dummy gate layer 106′. In some embodiments, during the planarization process, there has no other additional layers (such as, CMP stop layer and/or sacrificial layer) formed on the dummy gate layer 106′. In other words, the planarization (CMP) process is directly performed on the dummy gate layer 106′.

In general, the CMP process uses chemical and physical forces to smooth or planarize the workpiece (i.e., the dummy gate layer 106′ of the semiconductor structure shown in FIG. 7A/7B). In particular, the surface of workpiece need to be planarized (i.e., the upper surface of the dummy gate layer 106′) is brought into physical contact with a rotating polishing pad of a CMP apparatus while a slurry of chemical and abrasive components are introduced onto the workpiece. The rotating polishing pad and the slurry remove material from the dummy gate layer 106′ until the dummy gate layer 106 has a flat/planar surface. In some embodiments, the CMP process is performed using time mode, and a relatively hard polishing pad is selected to polish the top surface of the dummy gate layer 106′, such that the dummy gate layer 106 having substantially flat top surface is formed. In some embodiments, the polishing pad used for the CMP process of the dummy gate layer 106′ may be harder than the polishing pad used for the CMP process of the insulation material 102 (FIG. 3), but the disclosure is not limited thereto.

Referring to FIG. 8A and FIG. 8B to FIG. 9A and FIG. 9B, a patterning process is performed on the dummy gate layer 106 and the dielectric layer 105, so as to form a dummy gate dielectric layer 105 a and a dummy gate 106 a in the first region R1, and a dummy gate dielectric layer 105 b and a dummy gate 106 b in the second region R2. The patterning process may include one or more lithograph and etching processes. The dummy gate 106 a and the underlying dummy gate dielectric layer 105 a constitute a dummy gate structure DG1, while the dummy gate 106 b and the dummy gate dielectric layer 105 c constitute a dummy gate structure DG2. The dummy gate structure DG1 and the dummy gate structure DG2 may be continuous or non-continuous.

Referring to FIG. 1, FIG. 9A and FIG. 9B, the dummy gate structure DG1 extends along the direction D2 and across the fins 101 a, while the dummy gate structure DG2 extends along the direction D2 and across the fins 101 b. The top surface of the dummy gate structure DG1 (i.e. the top surface of the dummy gate 106 a) is substantially coplanar with the top surface of the dummy gate structure DG2 (i.e. the top surface of the dummy gate 106 b).

Referring to FIG. 10A and FIG. 10B, thereafter, spacers 108 a and 108 b are respectively formed on sidewalls of the dummy gate structures DG1 and DG2. In some embodiments, the spacer 108 a/108 b includes SiO₂, SiN, SiCN, SiOCN, SiC, SiOC, SiON, or the like, or combinations thereof. The spacers 108 a/108 b may be formed by suitable deposition process and etching process. For example, a spacer material is formed over the substrate to cover sidewalls and top surfaces of the dummy gate structures DG1 and DG2. Thereafter, an etching process, such as an etching back process is performed to remove excess portions (e.g., horizontal portions) of the spacer material, and remain the spacers 108 a and 108 b on sidewalls of the dummy gate structures DG1 and DG2. The spacers 108 a, 108 b are located on the fins 101 and the isolation structure 102 (not shown) and extend along the lengthwise direction D2 of the dummy gate structures DG1, DG2 to cover opposite sidewalls of the dummy gate structures DG1, DG2, respectively. The sidewall of the spacers 108 a, 108 b may be straight or slanted, or arced. It is noted that, the cross-sectional shape of the spacer 108 a/108 b is merely for illustration, and the disclosure is not limited thereto. The spacer 108 a/108 b may have any suitable shape.

After the spacers 108 are formed, source/drain (S/D) regions 109 are formed on opposite sides of the dummy gate structures DG1 and DG2 having spacers 108. The S/D regions 109 may be located in and/or on the fins 101 of the substrate 100. In some embodiments, the S/D regions 109 are strained layers (epitaxial layers) formed by epitaxial growing process such as selective epitaxial growing process. The formation of the S/D regions 109 may include the following processes: a recessing process is firstly performed on the fins 101, such that recesses are formed in the fins 101 on sides of the dummy gate structures DG1, DG2, and the strained layers are formed by selectively growing epitaxy layers from the fins 101 exposed in the recesses. In some embodiments, the strained layers include silicon germanium (SiGe), SiGeB, Ge, InSb, GaSb, InGaSb or combinations thereof for a P-type FinFET device. In alternative embodiments, the strained layers include silicon carbon (SiC), silicon phosphate (SiP), SiCP, InP, GaAs, AlAs, InAs, InAlAs, InGaAs or a SiC/SiP multi-layer structure, or combinations thereof for an N-type FinFET device. In some embodiments, the strained layers may be optionally implanted with an N-type dopant or a P-type dopant as needed. Alternatively or additionally, other suitable processes (e.g., implantation process) for forming S/D regions may also be used in the disclosure.

It is noted that, the shape and size of the S/D region 109 shown in the figures are merely for illustration, and the disclosure is not limited thereto. The S/D region 109 may have any suitable shape and size according to product design and requirement.

After the S/D regions 109 are formed, an etching stop layer 110 and a dielectric layer 112 are formed on the substrate 100 and laterally aside the dummy gate structures DG1, DG2 having spacers 108. The etching stop layer 110 may also be referred to as a contact etch stop layer (CESL), and is disposed between the substrate 100 (e.g. the S/D regions 109, the isolation structure 102, the fins 101 of the substrate 100) and the dielectric layer 112 and between the spacers 108 of the dummy gate structures DG1, DG2 and the dielectric layer 112. In some embodiments, the etching stop layer 110 includes SiN, SiC, SiOC, SiON, SiCN, SiOCN, or the like, or combinations thereof. The etching stop layer 110 may be formed by CVD, plasma-enhanced CVD (PECVD), ALD or the like.

The dielectric layer 112 is formed on the etching stop layer 110 and laterally aside the dummy gate structures DG1, DG2. The dielectric layer 112 includes a material different from that of the etching stop layer 110. In some embodiments, the dielectric layer 112 may also be referred to as an interlayer dielectric layer (ILD), such as ILD0. In some embodiments, the dielectric layer 112 includes silicon oxide, carbon-containing oxide such as silicon oxycarbide (SiOC), silicate glass, tetraethylorthosilicate (TEOS) oxide, un-doped silicate glass, or doped silicon oxide such as borophosphosilicate glass (BPSG), fluorine-doped silica glass (FSG), phosphosilicate glass (PSG), boron doped silicon glass (BSG), combinations thereof and/or other suitable dielectric materials. In some embodiments, the dielectric layer 112 may include low-k dielectric material with a dielectric constant lower than 4, extreme low-k (ELK) dielectric material with a dielectric constant lower than 2.5. In some embodiments, the low-k material includes a polymer based material, such as benzocyclobutene (BCB), FLARE®, or SILK®; or a silicon dioxide based material, such as hydrogen silsesquioxane (HSQ) or SiOF. The dielectric layer 112 may be a single layer structure or a multi-layer structure. The dielectric layer 112 may be formed by CVD, PECVD, FCVD, spin coating or the like.

In some embodiments, the etching stop layer 110 and the dielectric layer 112 may be formed by the following processes: after the S/D regions 109 are formed, an etching stop material layer and a dielectric material layer are formed over the substrate 100 to cover sidewalls and top surfaces of the dummy gate structures DG1, DG2; thereafter, a planarization process is performed to remove excess portions of the etching stop material layer and the dielectric material layer over the top surfaces of the dummy gate structures DG1, DG2, so as to expose the dummy gate structures DG1, DG2, thereby forming the etching stop layer 110 and the dielectric layer 112 laterally aside the dummy gate structures DG1, DG2. In some embodiments, the top surfaces of the dielectric layer 112 and the etching stop layer 110 are substantially coplanar with the top surfaces of the dummy gate structures DG1 and DG2.

Thereafter, a gate replacement process is performed to replace the dummy gate structures DG1 and DG2 with metallic gate structures 118 (FIG. 12). The details are described as below.

Referring to FIG. 11A and FIG. 11B, in some embodiments, the dummy gate structures DG1 and DG2 are removed by one or more etching processes, such as wet etching and/or dry etching. As such, a gate trench T_(a) defined by spacers 108 a is formed at the location previously occupied by the dummy gate structure DG1 in the first region R1, and a gate trench T_(b) defined by spacers 108 b is formed at the location previously occupied by the dummy gate structure DG2 in the second region R2. The gate trenches T_(a) and T_(b) expose upper portions of the fins 101 a, 101 b and the isolation structures 102 a, 102 b adjacent to the fins 101 a, 101 b, respectively.

Referring to FIG. 12A and FIG. 12B, thereafter, gate stacks 118 a and 118 b are formed in the gate trenches T_(a) and T_(b), respectively. In some embodiments, each of gate stacks 118 and 118 b includes a gate dielectric layer and a gate electrode on the gate dielectric layer. In some embodiments, the gate electrode is metallic gate electrode, and may include a work function layer and a metal filling layer on the work function metal layer. For example, the gate stack 118 a includes a gate dielectric layer 114 a, a work function layer 115 a and a metal filling layer 116 a, and the gate stack 118 b includes a gate dielectric layer 114 b, a work function layer 115 b and a metal filling layer 116 b.

The work function layer is configured to tune a work function of its corresponding FinFET transistor to achieve a desired threshold voltage Vt. Each of the work function layers 115 a, 115 b maybe an N-type work function metal layer or a P-type work function metal layer, and the work function layers 115 a and 115 b may be the same types of work function layers or different types of work function layers depending on the types of the to-be-formed FinFET transistors. In some embodiments, the P-type work function layer may include a metal with a sufficiently large effective work function and may include one or more of the following: TiN, WN, TaN, conductive metal oxide, and/or a suitable material, or combinations thereof. The N-type work function layer may include a metal with sufficiently low effective work function and may comprise one or more of the following: tantalum (Ta), titanium aluminide (TiAl), titanium aluminum nitride (TiAlN), tantalum carbide (TaC), tantalum carbide nitride (TaCN), tantalum silicon nitride (TaSiN), titanium silicon nitride (TiSiN), other suitable metals, suitable conductive metal oxide, or combinations thereof. Each of the work function layers 115 a and 115 b may be a single-layer structure or multi-layer structure. The metal filling layers 118 a and 118 b may include copper, aluminum, tungsten, cobalt (Co), or any other suitable metallic material, or the like or combinations thereof, respectively. In some embodiments, each of the gate electrodes may further include a seed layer, a barrier layer, other suitable layers or combinations thereof.

In some embodiments, the gate dielectric layers 114 a and 114 b are respectively disposed between the gate electrodes and the fins 101 a and 101 b, between the gate electrodes and the spacers 108 and 108 b, and between the gate electrodes and the isolation structure 102. The gate dielectric layers 114 a and 114 b surround the sidewalls and bottom surface of the work functional layers 115 a and 115 b of the gate electrodes, respectively. However, the disclosure is not limited thereto. In alternative embodiments, the gate dielectric layer may be not disposed between the gate electrode and the corresponding spacer. In some embodiments, the gate dielectric layer 104 may include silicon oxide, silicon nitride, silicon oxynitride, high-k dielectric materials, or combinations thereof. The high-k dielectric material may have a dielectric constant such as greater than about 4, or greater than about 7 or 10. In some embodiments, the high-k material includes metal oxide, such as ZrO₂, Gd₂O₃, HfO₂, BaTiO₃, Al₂O₃, LaO₂, TiO₂, Ta₂O₅, Y₂O₃, STO, BTO, BaZrO, HfZrO, HfLaO, HfTaO, HfTiO, combinations thereof, or a suitable material. In alternative embodiments, the gate dielectric layer 104 may optionally include a silicate such as HfSiO, LaSiO, AlSiO, combinations thereof, or a suitable material. In some embodiments, the gate stack 118 a/118 b may further include an interfacial layer between the gate dielectric layer 114 a/114 b and the corresponding fin 101. The interfacial layer may include an oxide such as silicon oxide, and may be formed by a thermal oxidation process.

In some embodiments, the gate stacks 118 a and 118 b are formed by the following processes. A gate dielectric material, a work function material, and a metal filling material are sequentially formed over the substrate 100 to cover the dielectric layer 112 and fill in the gate trenches T_(a) and T_(b), by suitable deposition processes such as CVD, PECVD, PVD, ALD, or the like or combinations thereof. Thereafter, a planarization process is performed to remove excess portions of the metal filling material, the work function material and the gate dielectric material over the top surface of the dielectric layer 112. In some embodiments, the top surfaces of the gate dielectric layers 114 a, the work function layer 115 a, 115 b, and the metal filling layers 116 a remained in the trenches T_(a) and T_(b) are substantially coplanar with each other and substantially coplanar with the top surface of the dielectric layer 112.

Referring to FIG. 12B, the gate stack 118 a, the spacers 108 a and the S/D regions 109 a constitute a FinFET transistor FT1 in the first region R1. The gate stack 118 b, the spacers 108 b and the S/D regions 109 b constitute a FinFET transistor FT2 in the first region R2. The FinFET transistor FT1 and the FinFET transistor FT2 may have the same conductivity types (N-type, or P-type) or different conductivity types.

Referring to FIG. 13A and FIG. 13B, in some embodiments, a dielectric layer 120 is then formed on the dielectric layer 112 to cover the dielectric layer 112 and the transistors FT1 and FT2. The material of the dielectric layer 120 may be selected from the same candidate materials of the dielectric layer 112. In some embodiments, the dielectric layer 120 may also be referred to as ILD1. In some embodiments, an etching stop layer (not shown) may further be disposed between the dielectric layer 112 and the dielectric layer 120.

In some embodiments, contacts 122 a and 122 b are formed to penetrate through the dielectric layers 120 and 112 to connect to the S/D regions 109 a and 109 b, respectively. In some embodiments, each of the contacts 122 a and 122 b includes a barrier layer (not shown) and a conductive layer (not shown) on the barrier layer. The barrier layer may surround sidewalls and/or bottom surface of the conductive layer. The barrier layer may include titanium, tantalum, titanium nitride, tantalum nitride, manganese nitride or combinations thereof. The conductive layer may include metal, such as tungsten (W), copper (Cu), Ru, Ir, Ni, Os, Rh, Al, Mo, Co, alloys thereof, combinations thereof or any metallic material with suitable resistance and gap-fill capability.

In some embodiments, the contacts 122 a and 122 b may be formed by the following processes: a patterning process is performed to remove portions of the dielectric layers 120, 112 and the etching stop layer 110, so as to define contact holes exposing portions of the S/D regions 109 a and 109 b; a barrier material layer and a conductive material layer are formed on the dielectric layer 120 to fill the contact holes; thereafter, a planarization process is performed to remove excess portions of the barrier material layer and the conductive material layer over the top surface of the dielectric layer 138, and the remained barrier layer and conductive layer in the contact holes constitute the contacts 122 a and 122 b. In some embodiments, the top surfaces of the contacts 122 a and 122 b are substantially coplanar with the top surface of the dielectric layer 120.

In some embodiments, the S/D regions 109 a and 109 b may include silicide layers thereon, and the contacts 122 a and 122 b may land on the silicide layers of the S/D regions 109 a, 109 b, respectively. In some embodiments, the silicide layers may be formed before forming the etching stop layer 110. In alternative embodiments, the silicide layers may be formed after the contact holes are defined and before forming the contacts 122 a and 122 b. In some embodiments, the silicide layers may respectively include nickel silicide (NiSi), cobalt silicide (CoSi), titanium silicide (TiSi), tungsten silicide (WSi), molybdenum silicide (MoSi), platinum silicide (PtSi), palladium silicide (PdSi), CoSi, NiCoSi, NiPtSi, Ir, PtIrSi, ErSi, YbSi, PdSi, RhSi, or NbSi, or combinations thereof, and may be formed by a self-aligned silicide (salicide) process.

Referring to FIG. 13A and FIG. 13B, a semiconductor device (which is a FinFET device) 200 is thus formed. The FinFET device 200 includes a first region R1 and a second region R2. A plurality of fins 101 a of the substrate 100, an isolation structure 102 a, and transistor FT1 are disposed within the first region R1. A plurality of fins 101 b of the substrate 100, an isolation structure 102 b and transistor FT2 are disposed within the second region R2.

In some embodiments, the fins 101 a and 101 b are parallel with each other and extend along the same direction D1. Each of the fins 101 a and 101 b has a length extending along the direction D1 and a width in the direction D2 perpendicular to the direction D1. In some embodiments, the spacing S1 between two adjacent fins 101 a is larger than the spacing S2 between two adjacent fins 101 b. The top surfaces of the fins 101 a may be substantially coplanar with the top surfaces of the fins 101 b. In some embodiments, the fins 101 a and 101 b have the same heights. Herein, a height of a fin refers to the height of the fin protruding above the top surface TS of the substrate 100 (i.e. the vertical distance between the top surface of the fin and the top surface TS of the substrate) in the direction D3.

The isolation structures 102 a and 102 b are disposed on the substrate 100 and laterally covering portions of the fins 101 a and 101 b, respectively. The gate stack 118 a is disposed on and across the fins 101 a and the isolation structure 102 a within the first region R1, and the gate stack 118 b is disposed on and across the fins 101 b and the isolation structure 102 b within the second region R2. In some embodiments, the gate stacks 118 a and 118 b respectively extend along the direction D2 (i.e. the widthwise direction of the fins 101 a and 101 b). The gate stacks 118 a and 118 b may be continuous or non-continuous in the direction D2.

In some embodiments, the top surface of the isolation structure 102 a is lower than the top surface of the isolation structure 102 b, and the height H1 of the isolation structure 102 a is less than the height H2 of the isolation structure 102 b. The isolation structures 102 a and 102 b respectively include a portion EP₁ and a portion EP₂ laterally sandwiched between two adjacent fins 101 a, 101 b. In some embodiments, the width of the portion EP₁ of the isolation structure 102 a is substantially equal to the spacing S1 of the fins 101 a, and the width of the portion EP₂ of the isolation structure 102 b is substantially equal to the spacing S2 of the fins 101 b. In other words, the width of the portion EP₁ is larger than the width of the portion EP₂. That is to say, the portion EP₂ of the isolation structure 102 b is narrower and higher (or thicker) than the portion EP₁ of the isolation structure 102 a.

Still referring to FIG. 13A and FIG. 13B, each of the fins 101 a includes a bottom portion BP₁ and an upper portion UP₁ on the bottom portion BP₁. The sidewalls of the bottom portion BP₁ are covered by and in contact with the isolation structure 102 a, and the sidewalls and top surface of the upper portion UP₁ are covered (surrounded) by and in contact with the gate stack 118 a. In other words, the upper portion UP₁ is embedded in the gate stack 118 a. Similarly, each of the fins 101 b includes a bottom portion BP₂ laterally covered by the isolation structure 102 b, and an upper portion UP₂ having top surface and sidewalls wrapped by the gate stack 118 b.

In some embodiments, the height of the lower portion BP₁ of the fin 101 a (which is substantially equal to the height H1 of the isolation structure 102 a) is less than the height of the lower portion BP₂ of the fin 101 b (which is substantially equal to the height H2 of the isolation structure 102 b). The height H3 of the upper portion UP₁ of the fin 101 a is larger than the height H4 of the upper portion UP₂ of the fin 101 b. In some embodiments, the width of the fin 101 a may be substantially equal to or different from the width of the fin 101 b. In some embodiments, the volume of the upper portion UP₁ of the fin 101 a is larger than the volume of the upper portion UP₂ of the fin 101 b. The contact area between the fin 101 a and the gate stack 118 a may be larger than the contact area between the fin 101 b and the gate stack 118 b. However, the disclosure is not limited thereto.

From another point of view, the channel region (i.e. the upper portion UP₁ wrapped by the gate stack 118 a) of fin 101 a has a height larger than a height of the channel region (i.e. the upper portion UP₂ wrapped by the gate stack 118 b) of the fin 101 b. The top surface of the channel region of the fin 101 a is substantially coplanar with the top surface of the channel region of the fin 101 b, and a bottom point of the channel region of the fin 101 a is lower than a bottom point of the channel region of the fin 101 b. In some embodiments, the channel region of the fin 101 a has a larger volume than the channel region of the fin 101 b. The contact area between the channel region of the fin 101 a and the gate stack 118 a may be larger than the contact area between the channel region of the fin 101 b and the gate stack 118 b.

In some embodiments, the gate stack 118 a has a first bottom surface BS_(a1) (i.e. bottommost surface) in contact with the top surface TS1 of the isolation structure 102 a, a second bottom surface BS_(a2) in contact with the top surface of the fin 101 a, and a top surface TS_(a1) over the top surface of the fin 101 a. The gate stack 118 b has a first bottom surface BS_(b1) (i.e. bottommost surface) in contact with the top surface TS2 of the isolation structure 102 b, a second bottom surface BS_(b2) in contact with the top surface of the fin 101 b, and a top surface TS_(b1) over the top surface of the fin 101 b. In some embodiments, the first bottom surface BS_(a1) of the fin 101 a may be lower than the first bottom surface BS_(b1) of the fin 101 b. The second bottom surface BS_(a2) of the fin 101 a may be substantially coplanar with the second bottom surface BS_(b2) of the fin 101 b. The top surface TS_(a1) of the gate stack 118 a may be substantially coplanar with the top surface TS_(b1) of the gate stack 118 b.

In other words, the gate stack 118 a has a height H5 and a height H7. The height H5 of the gate stack 118 a is defined by a vertical distance between the top surface TS_(a1) and the bottom surface BS_(a1) of the gate stack 118 a in the direction D3, or between the top surface TS_(a1) of the gate stack 118 a and the top surface TS1 of the isolation structure 102 a. The height H7 of the gate stack 118 a is defined by a vertical distance between the top surface TS_(a1) and the bottom surface BS_(a2) of the gate stack 118 a in the direction D3, or between the top surface TS_(a1) of the gate stack 118 a and the top surface of the fin 101 a. Similarly, the gate stack 118 b has a height H6 and a height H8. The height H6 of the gate stack 118 a is defined by a vertical distance between the top surface TS_(b1) and the bottom surface BS_(b1) of the gate stack 118 b in the direction D3, or between the top surface TS_(b1) of the gate stack 118 b and the top surface TS2 of the isolation structure 102 b. The height H8 of the gate stack 118 b is defined by a vertical distance between the top surface TS_(b1) and the bottom surface BS_(b2) of the gate stack 118 b in the direction D3, or between the top surface TS_(b1) of the gate stack 118 b and the top surface of the fin 101 b. The heights H7 and H8 may be also referred to as the gate heights of the gate stacks 118 and 118 b, respectively. Herein, the term “gate height” refers to the height of the portion of the gate directly on the top surface of fin.

Still referring to FIG. 13A and FIG. 13B, in some embodiments, the height H5 of the gate stack 118 a is larger than the height H6 of the gate stack 118 b, while the height H7 of the gate stack 118 a is substantially equal to the height H8 of the gate stack 118 b. For example, the height H7/H8 may range from 10 nm to 30 nm. The height H5 may range from 110 nm to 130 nm. The height H6 may range from 60 nm to 90 nm. The ratio of the height H5 to the height H6 may range from 1.4 to 1.9. The height ratio in such range is primarily caused by the difference between spacings S1 and S2. If the ratio range is less than the lower limit, the height difference may be caused by processing error instead of the different spacings of fins. If the ratio range is larger than the upper limit, the difficulty of the previous CMP process for planarizing the dummy gate structure (FIG. 7 to FIG. 8) may be increased. In some embodiments, the gate stack 118 a includes a portion GP₁ located on the portion EP₁ of the isolation structure 102 a and laterally between two adjacent fins 101 a, and the gate stack 118 b includes a portion GP₂ located on the portion EP₂ of the isolation structure 102 b and laterally between two adjacent fins 101 b. In some embodiments, the portion GP₁ of the gate stack 118 a is wider and thicker than the portion GP₂ of the gate stack 118 b.

Referring to FIG. 13B, in some embodiments, parasitic capacitances may be formed between gate stacks 118 a, 118 b and the contacts 122 a, 122 b, respectively. In some embodiments, since the gate height H8 of the gate stack 118 b is substantially equal to the gate height H7 of the gate stack 118 a, the parasitic capacitance that may be formed between the gate stack 118 b and the contact 122 b may be substantially equal to the parasitic capacitance that may be formed between the gate stack 118 a and the contact 122 a, but the disclosure is not limited thereto. In other words, no excess parasitic capacitance happens on the gate stack 118 b over the higher isolation structure 102 b compared to the gate stack 118 a over the lower isolation structure 102 a.

In the embodiments of the disclosure, the fins having different spacings are formed, thereby causing the isolation structures in different regions have different height. During the CMP process for planarizing the dummy gate material, the formations of CMP stop layer and/or sacrificial layer on the dummy gate material are omitted. The dummy gate layer is directly planarized by the CMP process using time mode, and the CMP process uses a relatively hard polishing pad, so as to form a dummy gate layer with substantially flat top surface. As such, the cost of manufacturing is reduced, and the global and/or local gate height control is improved. In some embodiments, the gate heights on the different fins are controlled to be substantially the same as each other. No excess gate height happened on fins having different pattern (e.g., spacing), thereby avoiding excess parasitic capacitance generated between excess gate and the contact. Accordingly, the device performance is improved.

In accordance with some embodiments of the disclosure, a FinFET includes a substrate, a first gate stack and a second gate stack. The substrate has a first fin and a second fin. The first gate stack is across the first fin and extends along a widthwise direction of the first fin. The second gate stack is across the second fin and extends along a widthwise direction of the second fin. A bottommost surface of the first gate stack is lower than a bottommost surface of the second gate stack, and a first gate height of the first gate stack directly on the first fin is substantially equal to a second gate height of the second gate stack directly on the second fin.

In accordance with alternative embodiments of the disclosure, a FinFET device includes a substrate having first fins and second fins, a first isolation structure, a second isolation structure, a first gate stack and a second gate stack. A spacing between neighboring fins of the first fins is larger than a spacing between neighboring fins of the second fins. The first isolation structure is disposed on the substrate and between the neighboring fins of the first fins. The second isolation structure is disposed on the substrate and between the neighboring fins of the second fins. The first gate stack is disposed over the substrate and across the first fins and the first isolation structure. The second gate stack is disposed over the substrate and across the second fins and the second isolation structure. A top surface of the first gate stack is substantially coplanar with a top surface of the second gate stack.

In accordance with some embodiments of the disclosure, a method of forming a FinFET device includes: providing a substrate; patterning the substrate to form first fins within a first region and second fins within a second region, wherein the first fins are formed to have a first spacing between neighboring fins, the second fins are formed to have a second spacing between neighboring fins, and the first spacing is larger than the second spacing; forming a first isolation structure covering lower portions of the first fins, and a second isolation structure covering lower portions of the second fins; forming a dummy gate material to cover the first fins, the first isolation structure, the second fins and the second isolation structure; and performing a planarization process on the dummy gate material using time mode, such that the dummy gate material remained within the first region has a top surface substantially coplanar with a top surface of the dummy gate material remained within the second region.

The foregoing outlines features of several embodiments so that those skilled in the art may better understand the aspects of the present disclosure. Those skilled in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions, and alterations herein without departing from the spirit and scope of the present disclosure. 

What is claimed is:
 1. A FinFET device, comprising: a substrate having a first fin and a second fin; a first gate stack across the first fin and extending along a widthwise direction of the first fin; and a second gate stack across the second fin and extending along a widthwise direction of the second fin; wherein a bottommost surface of the first gate stack is lower than a bottommost surface of the second gate stack, and a first gate height of the first gate stack directly on the first fin is substantially equal to a second gate height of the second gate stack directly on the second fin.
 2. The FinFET device of claim 1, wherein a channel region of the first fin has a height larger than a height of a channel region of the second fin.
 3. The FinFET device of claim 1, wherein a top surface of the first gate stack is substantially coplanar with a top surface of the second gate stack.
 4. The FinFET device of claim 1, wherein a contact area between the first gate stack and the first fin is larger than a contact area between the second gate stack and the second fin.
 5. The FinFET device of claim 1, further comprising: a first isolation structure, disposed on the substrate and laterally covering a lower portion of the first fin; and a second isolation structure, disposed on the substrate and laterally covering a lower portion of the second fin, wherein a top surface of the first isolation structure is lower than a top surface of the second isolation structure.
 6. The FinFET device of claim 5, wherein a height of the first gate stack directly on the first isolation structure is larger than a height of the second gate stack directly on the second isolation structure.
 7. The FinFET device of claim 1, further comprising: a first source/drain (S/D) region beside the first gate stack; a second S/D region beside the second gate stack; a first contact, connected to the first S/D region; and a second contact, connected to the second S/D region, wherein a parasitic capacitance between the first gate stack and the first contact is substantially equal to a parasitic capacitance between the second gate stack and the second contact.
 8. A FinFET device, comprising: a substrate having first fins and second fins, wherein a spacing between neighboring fins of the first fins is larger than a spacing between neighboring fins of the second fins; a first isolation structure, disposed on the substrate and between the neighboring fins of the first fins. a second isolation structure, disposed on the substrate and between the neighboring fins of the second fins; a first gate stack, disposed over the substrate and across the first fins and the first isolation structure; and a second gate stack, disposed over the substrate and across the second fins and the second isolation structure, wherein a top surface of the first gate stack is substantially coplanar with a top surface of the second gate stack.
 9. The FinFET device of claim 8, wherein the second isolation structure is narrower and higher than the first isolation structure.
 10. The FinFET device of claim 8, wherein a height of lower portions of the first fins that are covered by the first isolation structure is less than a height of lower portions of the second fins that are covered by the second isolation structure.
 11. The FinFET device of claim 8, wherein one of the first fins comprises a first upper portion wrapped by the first gate stack; one of the second fins comprises a second upper portion wrapped the second gate stack; and a height of the first upper portion is larger than a height of the second upper portion.
 12. The FinFET device of claim 8, wherein a contact area between a channel region of the first fins and the first gate stack is larger than a contact area between a channel region of the second fins and the second gate stack.
 13. The FinFET device of claim 8, wherein a bottom surface of the first gate stack contacting the first isolation structure is lower than a bottom surface of the second gate stack contacting the second isolation structure.
 14. The FinFET device of claim 8, wherein a portion of the first gate stack between the neighboring fins of the first fins is wider and thicker than a portion of the second gate stack between the neighboring fins of the second fins.
 15. A method of forming a FinFET device, comprising: providing a substrate; patterning the substrate to form first fins within a first region and second fins within a second region, wherein the first fins are formed to have a first spacing between neighboring fins, the second fins are formed to have a second spacing between neighboring fins, and the first spacing is larger than the second spacing; forming a first isolation structure covering lower portions of the first fins, and a second isolation structure covering lower portions of the second fins; forming a dummy gate material to cover the first fins, the first isolation structure, the second fins and the second isolation structure; and performing a planarization process on the dummy gate material using time mode, such that the dummy gate material remained within the first region has a top surface substantially coplanar with a top surface of the dummy gate material remained within the second region.
 16. The method of claim 15, wherein forming the first isolation structure and the second isolation structure comprises: forming an insulation material to cover the first fins and the second fins; and performing an etching process to recess the insulation material, so as to expose upper portions of the first fins and upper portions of the second fins, wherein a removal amount of the insulation material within the first region is larger than a removal amount of the insulation material within the second region due to the larger spacing between the first fins.
 17. The method of claim 15, wherein the first isolation structure is formed to have a top surface lower than a top surface of the second isolation structure, and a first top surface of the dummy gate material within the first region is lower than a second top surface of the dummy gate material within the second region before performing the planarization process.
 18. The method of claim 15, wherein after performing the planarization process, further comprising: patterning the dummy gate material into a first dummy gate structure within the first region and a second dummy gate structure within the second region; and replacing the first dummy gate structure and the second dummy gate structure with a first gate stack and a second gate stack, respectively, wherein a top surface of the first gate stack is formed to be substantially coplanar with a top surface of the second gate stack.
 19. The method of claim 18, wherein a gate height of the first gate stack directly over the first fin is substantially equal to a gate height of the second gate stack directly over the second fin.
 20. The method of claim 18, wherein a height of the first gate stack directly over the first isolation structure is higher than a height of the second gate stack directly over the second isolation structure. 